Add tab containers

[LondonClass]

Desired features A tab container that can switch between different windows by clicking on the tab.

Sample code

import pygame

from pygame_gui import UIManager, UI_BUTTON_PRESSED
from pygame_gui.elements import UIButton, UITabContainer

pygame.init()


pygame.display.set_caption('Quick Start')
window_surface = pygame.display.set_mode((800, 600))
manager = UIManager((800, 600))

background = pygame.Surface((800, 600))
background.fill(manager.ui_theme.get_colour('dark_bg'))

tab_container = UITabContainer(relative_rect=pygame.Rect(50, 50, 700, 500), manager=manager)

container_1 = tab_container.get_container(tab_container.add_tab("Tab1"))
container_2 = tab_container.get_container(tab_container.add_tab("Tab2"))

hello_button_1 = UIButton((250, 180), 'Hello1', container=container_1, command=lambda: print("Hello1!"))
hello_button_2 = UIButton((350, 280), 'Hello2', container=container_2, command=lambda: print("Hello2!"))

clock = pygame.time.Clock()
is_running = True

while is_running:
    time_delta = clock.tick(60)/1000.0
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            is_running = False
        manager.process_events(event)

    manager.update(time_delta)

    window_surface.blit(background, (0, 0))
    manager.draw_ui(window_surface)

    pygame.display.update()

Screenshot

I still don't quite understand what features I want and what interfaces should be opened. So I send the PR and see what everyone thinks.

Fixes #102

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 22.00000% with 117 lines in your changes are missing coverage. Please review.

Project coverage is 95.34%. Comparing base (e7a9dd5) to head (fe0f020).

:exclamation: Current head fe0f020 differs from pull request most recent head 15cc2ba. Consider uploading reports for the commit 15cc2ba to get more accurate results

Files	Patch %	Lines
pygame_gui/elements/ui_tab_container.py	19.71%	114 Missing :warning:
pygame_gui/core/drawable_shapes/drawable_shape.py	50.00%	2 Missing :warning:
pygame_gui/elements/ui_button.py	66.66%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #529      +/-   ##
==========================================
- Coverage   96.33%   95.34%   -0.99%     
==========================================
  Files          88       89       +1     
  Lines       13013    13159     +146     
==========================================
+ Hits        12536    12547      +11     
- Misses        477      612     +135     

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[MyreMylar]

Currently looks like this:

I'm going to merge it - tagged in the API docs as experimental, we'll see how people get on with it and see if anythign needs tweaking.

Thanks for the PR!